This invention relates to marine drilling platforms for the production of hydrocarbons, and, more particularly, to a relatively small and inexpensive platform.
The use of platforms for the development of hydrocarbon reserves in deep water is extremely expensive. Often, small reservoirs are bypassed because of the lack of economic return because of the high cost of a platform to develop them.
One alternative to the use of deepwater platforms is the subsea completion. However, this method is also relatively expensive and requires some type of surface facility to process and treat the hydrocarbons.
A similar problem exists in the development of fringe areas of a reservoir which cannot be developed from a major platform. In addition, there is often some uncertainty as to the productivity of what may be a relatively large reserve area and further information is desirable prior to the final design and/or commitment of a major platform.
The typical platform in use today is the battered leg platform. The cost of such platform rises very steeply as the depth of the water increases. At greater depths, the vertically moored platform (in which the legs of the platform are essentially parallel) is less expensive than the battered leg platform. The vertically moored platform is described in U.S. Pat. Nos. 3,559,410, issued to Blenkarn and Dixon, and 3,648,638, issued to Blenkarn. While such an arrangement can be less expensive than the conventional battered leg platform, the costs are still high and such platforms cannot be used to economically develop relatively small reserves.
A number of platform arrangements providing alternatives to major platforms have been proposed. A shallow-water platform using a single riser caisson, but with the wells drilled outside the caisson, is proposed in U.S. Pat. No. 3,881,549, issued to Thomas, May 6, 1975. An unusual single caisson arrangement is proposed in U.S. Pat. No. 3,364,684, issued to Sandberg, Jan. 23, 1968. Arrangements have also been proposed in which the wells are completed at an intermediate depth (rather than either above the water level or on the ocean floor). Such arrangements are described in U.S. Pat. No. 3,556,210, issued to Johnson, Jan. 19, 1971, U.S. Pat. No. 3,470,838, issued to Daniell, Oct. 7, 1969, and U.S. Pat. No. 3,380,520, issued to Pease, Apr. 30, 1968. These intermediate depth well arrangements avoid the problem of divers having to work at extreme depths, but the use of the divers, even at these intermediate depths is still quite expensive.
None of the prior art methods provide a proven, economical method of developing hydrocarbon reserves when a limited number of wells need be drilled in deepwater location.